Regulation of Gene Expression using siRNA
siRNA siRNA is can mean small interfering RNA or short interfering RNA, and are short RNA molecules of about 20-25 base pairs in length. SiRNA is used in the RNAi (RNA interference) pathway. How siRNA works is by complementary base pairing to a target mRNA strand, once the mRNA is partially double stranded the mRNA is targeted for degredation and will not be expressed. The role of siRNA occurs naturally, however synthetic siRNA molecules can be created in order to target the translation of mRNA molecules with a high degree of specificity. SiRNAs are created from long dsRNA and small hairpin RNAs by the Dicer enzyme, and can also be introduced to a cell by transfection. Due to the specificity with which it is able regulate gene expression makes it a useful tool for knocking out gene function, thus making it possible to discover the gene's role. History The role of siRNA was first discovered in plants by David Baulcombe and colleagues at the Sainsbury Laboratory, and was reported in Science in 1999. Soon after, Thomas Tuschl and colleagues reported in Nature that synthetic siRNAs could induce RNAi in mammalian cells. These discoveries led to increased interest in siRNA as a tool for biomedical research. siRNA's As An Antiviral Defense Mechanism in Plants siRNAs can be used as an antiviral defense mechanism in plants. This mechanism uses the virus mediated dsRNA, which is used to make pathogenic proteins, and creates vsiRNA (virus mediated siRNA). The vsiRNAs are then used to target and inhibit gene expression of viral proteins. This was seen for the first time in 2001 when Scorza et al. (2001) used RNAi to produce Plum Pox Virus resistant species of woody perennial. The RNAi was used to interfere wtih the gene expression of the PPV coat protein gene. The gene expression being regulated in this example is the Plum Pox Virus protein coat gene. The role of this gene is to provide the necessary protein coat for PPV so that the viral genetic information is protected for the cellular environment. The plant is using siRNA to silence gene expression of the PPV protein coat gene, by complementary binding to the PPV protein coat mRNA, and thus targeting the mRNA for degredation. The viral mediated dsRNA is the stimulus that affects this gene expression. The reason why it is necessary to regulate viral gene expression in this manner is due to the high degree of specificity of siRNA. The specificity of the vsiRNA makes it possible for the affected cell to inhibit gene expression of the virus, while not influencing its own gene expression. References Younis A, Siddique MI, Kim CK, Lim KB. RNA Interference (RNAi) Induced Gene Silencing: A Promising Approach of Hi-Tech Plant Breeding.Int J Biol Sci 2014; 10(10):1150-1158. doi:10.7150/ijbs.10452. Available from http://www.ijbs.com/v10p1150.htm Scorza, Ralph, and Al. Et. "Ovid: Welcome to OvidSP." Ovid: Welcome to OvidSP. Transgenic Research, June 2001. Web. 22 Oct. 2014. . "Small Interfering RNA." Wikipedia. Wikimedia Foundation, 19 Oct. 2014. Web. 22 Oct. 2014. .